As a semiconductor device used in a power converter such as an inverter, there are a MOS (Metal-Oxide-Semiconductor) transistor, an IGBT (Insulated Gate Bipolar Transistor), a diode etc. The diode is used for a reflux flow, being connected anti-parallel to the IGBT. Accordingly, the diode in this case is referred to as a FWD (Free Wheeling Diode).
In the improvement of characteristics of a power converter, it is important to improve the characteristics of the FWD, for example, electric characteristics such as a switching time, an ON voltage and a leak current, along with the improvement of characteristics of the MOS transistor and the IGBT.